Preliminary findings from the first grant period indicate that deficits occur in elderly subjects (N=8) compared to young subjects (N=14) to detect tactile (single skin indentations) and vibratory (40 and 250 Hz) stimuli applied to their hands. Elderly subjects showed great intersubject variability in detecting the tactile stimuli. Sensitivity to warm, cool, and noxious heat applied to the hand did not differ in the young and elderly subjects. When applied to the sole of the foot, elderly subjects were less sensitive to all stimuli than the young subjects. Specific aims include: (1) Continuation of the survey of somatosensory acuity to increase the subject population to N=20. (2) Use a magnitude matching technique to measure the growth in intensity of the several sensations to suprathreshold stimulus intensities in young and elderly subjects. (3) The lack of significant differences between young and elderly in thresholds of warm, cool, and heat-pain sensations are consistent with the hypotheses that the 2-alternative forced-choice method is not subject to potential non-sensory biases. Signal detection methods will be used to seek and measure such biases. Potential differences between young and elderly subjects in the decision making process will be assessed by manipulation of the length of the stimulus-decision period. (4) The small to absent differences in sensitivity of young and elderly subjects to the several modes of stimulation of the hand compared to the large differences when applied to the foot suggest diminished function of the elderly primary conducting system. The hypothesis is to be investigated by recording compound action potentials (CAP), percutaneously in the sciatic, median, and ulnar nerves evoked by mechanical and electrical stimuli applied to a digit. Comparisons are to be made of latencies, amplitude and temporal dispersion of the CAPs. (5) Measurements of two-point thresholds made by traditional means are capricious in size, for several reasons, in young subjects and frequently unobtainable in elderly subjects. A more appropriate method to measure touch acuity would be detection of the existence of texture. The apparatus proposed is described.